In the automotive field, position sensors are well known in the art. A typical arrangement has a single exciter and multiple receiving coils positioned at some gap apart from each other such that a coupler creates eddy currents in the receiving coil under constant excitation. Other position sensors known in the art function as an air-core transformer. A position sensor that functions as the air-core transformer, at its simplest, includes an excitation coil, an output coil, and a sensor coil. The excitation coil is electrically excited with an excitation signal. The output coil is inductively coupled to the excitation coil upon electrical excitation of the excitation coil. The sensor coil is electrically shorted and upon electrical excitation of the excitation coil, is inductively coupled to at least one of the excitation coil or the output coil.
Other known variations of position sensors include a signal source, an excitation coil, an output coil or a plurality of differently wound output coils, and a sensor coil. The signal source is operable to supply an excitation signal. The excitation coil is coupled to receive the excitation signal. The output coil is inductively coupled to the excitation coil upon excitation of the excitation coil with the excitation signal, to thereby supply an output signal. The sensor coil is electrically shorted and upon excitation of the excitation coil with the excitation signal, is inductively coupled to at least one of the excitation coil or the output coil, thus the output signal varies with movement of the sensor coil.
Example inductive position sensing units such as those disclosed in U.S. Pat. Nos. 7,538,544, 7,446,443, 8,098,061 and 8,508,242 may disclose a constant powered oscillator used to power the position sensor. However, as seen in these oscillating position sensors which, generally, include an air gap, there is a large amount of radiated emissions that occur at the operating frequency. As a result, emission standards have been established to set peak and average emission limits. The peak emission limit is set by the maximum amplitude of the oscillation, whereas the average is set by how long the oscillation is active over a set amount of time. Generally, for sampling and complexity reasons, the DC power oscillator is constantly on; however, with the new emission standards, particularly in Europe, there is peak and average emission limits between the AM radio and a 5 MHz frequencies that position sensors must now not exceed to pass the standards.
As such, it is desirable to control the inductive position sensor's peak and average emission values without comprising performance.